The present invention relates to the discovery of new solvents for poly(iminoimidazolidinediones), poly(parabanic acid) resins (PPA) and copolymers of the iminoimidazolidinediones and parabanic acids. More specifically certain poly(parabanic acids) and their precursors, poly(iminoimidazolidinediones) and copolymers of the precursors and poly(parabanic acid) are soluble in epichlorohydrin, the bromo and iodo analogues thereof and glycidyl acrylate.
In the prior art the solvents employed for poly (parabanic acids) have been dipolar aprotic organic materials such as dimethylformamide, diethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N,N-dimethylpropionamide, N,N-dimethylbutyramide, N-methylpyrrolidone, N-ethylpyrrolidone, hexamethylphosphoramide, dimethylsulfoxide and the like.
Dimethylformamide and other oganic amide solvents normally contain amine impurities or degradation products such as from the hydrolysis of the amides by water present as an impurity. Even careful and rigorous purification of the amides prior to use and the use of extreme precautions to maintain them in an anhydrous state are rarely successful to prevent the absorption of atmospheric moisture.
The presence of residual or in situ generated amine impurities have been found to be detrimental to poly(parabanic acids) in solution and after casting therefrom. The detrimental effect of the base amine impurities is manifested by molecular weight degradation of the polymer.
Among the advantages obtained by the present invention are (1) complete removal of the solvents from the polymer occurs at lower temperatures and/or at higher rates, (2) the solvents are easily recovered and purified, (3) there are no basic contaminates such as amine impurities, which can attack the poly(parabanic acids) and (4) the solvents are insoluble in water so that water absorption is not a problem as it is with dimethylformamide and the other dipolar aprotic solvents. Furthermore, the present solvents have the advantage that they are superior in applications, such as casting film, coating surfaces and wires, forming laminates, in adhesive formulations, fiber spinning, spray drying and the like, where solvent evaporation is necessary. These and other advantages and features of the present invention will be seen in the following descriptions.